The invention is in the field of multiple photoflash lamp units, such as planar arrays of the FlipFlash type.
U.S. Pat. No. 3,937,946 to Weber discloses a FlipFlash type of flash array having a group of four lamps in the upper half of the array and another group of four lamps in the lower half of the array. A connector tab at the bottom of the array has first and second connection terminals connected to the upper group of lamps and their sequential firing circuitry, and another connector tab at the top of the array has first and second connection terminals connected to the lower group of lamps and their sequential firing circuitry. The flash array is used by plugging one of its connector tabs into a camera socket having first and second contacts which contact respectively with the connector tabs' terminals and which are connected to a firing pulse source, and the "upper" group of lamps, which are farther from the camera's lens axis than the "lower" group of lamps, are flashed, one at a time, for taking four flash pictures. The array is then turned around and the other connector tab is plugged into the socket, for four more flash pictures. By thus flashing only lamps that are spaced away from the lens axis, the undesirable "red-eye" effect is reduced, which can occur if the flashing lamp is near the lens axis so that its light illuminates a part of a subject's retina that is seen in the picture.
The flash lamps in the FlipFlash array are high voltage types, requiring about 1,000 volts (at low energy) for flashing. The firing pulse, of a few thousand volts, can be produced by a small piezoelectric element in the camera and which is impacted in synchronism with the opening of the shutter. The flash lamps can become accidentally flashed by electrostatic electricity when the array is handled by a person who is electrostatically charged with a few thousand volts, unless the array is properly designed. A technique for reducing the possibility of electrostatic flashing of the lamps and disclosed in U.S. Pat. Nos. 3,980,875 and 3,980,876 to Cote, is to provide shielding in the array around, or partly around, the lamps and circuitry, the connector terminals being arranged so that the first one of them is more readily touched than the second when the array is handled by a person, this first terminal being connected electrically to the shield in the array. Thus, any electrostatic charge applied to the terminal areas of the array will be carried, via the more readily touched first terminal, to the shielding and be dissipated into surrounding space and thus is prevented from causing lamps to flash. The first (more readily touched) terminal and the circuitry to which it is connected are conveniently referred to as "electrical ground" of the array, the second terminal being the " electrically hot" terminal.
U.S. Pat. No. 3,952,320 to Blount discloses a FlipFlash type of array having means for preventing accidental flashing of lamps in the lower part of the array when lamps are flashed in the upper part of the array. Such accidental flashing could occur due to stray capacitance coupling of the firing pulse to the circuitry for the lower group of lamps, from the conductor carrying the firing pulse from the plugged-in lower "hot" terminal to the sequencing circuitry for the upper group of lamps. To prevent this accidental flashing, a third connector terminal is provided on each connector tab and is electrically connected in the array to the "hot" terminal of the other connector tab. The camera socket is provided with a third contact for contacting the third terminal of the plugged-in array tab, this third socket contact being connected electrically to the electrical ground first socket contact. Thus, when the array is connected to the camera socket, the third terminal becomes connected to the "ground" terminal, thus short-circuiting enough of the circuitry of the lower group of lamps to prevent the aforesaid accidental flashing.
Some camera manufacturers have found it expedient to make the two electrical ground contacts of the socket from a single piece of metal, and as a result these two contacts might not be sufficiently resilient with respect to each other to reliably individually contact against the respective first and third terminals of the plugged-in connector tab. As a result, there have been instances wherein the electrical ground first terminal of the array was not contacted, resulting in a firing pulse being applied only across the two "hot" terminals of the array and causing two lamps to flash simultaneously; the desired one in the upper group and an undesired one in the lower group.